Wells are generally drilled into the ground to recover natural deposits of hydrocarbons and other desirable materials trapped in geological formations in the Earth's crust. A well is typically drilled using a drill bit attached to the lower end of a drill string. The well is drilled so it penetrates the subsurface formations containing the trapped materials for recovery of the trapped materials. The bottom end of the drill string conventionally includes a bottom-hole assembly that has sensors, control mechanisms, and associated circuitry and electronics. As the drill bit is advanced through the formation, drilling fluid (e.g., drilling mud) is pumped from the surface through the drill string to the drill bit. The drilling fluid exits the drill bit and returns to the surface. The drilling fluid cools and lubricates the drill bit and carries the drill cuttings back to the surface. Electrical power is typically used to operate the sensors, circuitry and electronics in the bottom-hole assembly. Electrical power is conventionally provided by batteries in the bottom-hole assembly. Drawbacks to batteries include maintaining a charge in the batteries. Electrical power has also been conventionally provided by pipe internal mud flow, which may be directed through a turbine with an alternator. Drawbacks to the turbine include location of the turbine in the center of the mud flow, which will not allow downhole tools to pass the turbine.
Consequently, there is a need for an improved method of providing electrical power downhole.